A radioactive tracer is a small amount of a radiopharmaceutical designed to travel to a particular organ, tissue or type of cell. It may be injected into a vein, swallowed or inhaled, depending on the examination. A specialised scanner detects the radiation emitted by the tracer and creates images showing where it has accumulated. This can provide information about processes such as blood flow, metabolism or cellular activity that may not be visible on conventional imaging alone.

Diagnostic nuclear medicine uses relatively small amounts of radioactive material to create images and assess how tissues or organs are functioning. Common diagnostic approaches include PET and SPECT imaging. Therapeutic nuclear medicine uses radiopharmaceuticals designed to deliver a higher radiation dose directly to specific cells or tissues, helping to destroy or control disease. Some treatments target particular cancer cells, while radioactive iodine can be used for certain thyroid conditions.

Common nuclear medicine examinations include PET scans, SPECT scans, bone scans, thyroid and parathyroid scans, HIDA scans to assess the gallbladder and bile ducts, and nuclear cardiac stress tests. The appropriate examination depends on what the doctor needs to evaluate. PET and SPECT may also be combined with CT or, in selected settings, MRI to provide both functional and anatomical information.

Therapeutic nuclear medicine may be considered when a radiopharmaceutical can specifically reach the cells or tissues affected by a disease. Examples include radioactive iodine treatment for certain thyroid conditions and targeted radiopharmaceutical therapies for selected cancers, including some neuroendocrine and prostate cancers. Suitability depends on the type and extent of disease, whether the target is present, previous treatments and the patient's overall health. In some cancer therapies, diagnostic imaging is first used to determine whether the disease is likely to respond to the treatment.

Preparation varies considerably depending on the examination or treatment. Some scans require fasting, while others may require specific instructions about medicines, blood sugar levels or physical activity. Patients should tell the nuclear medicine team about all medicines and supplements they take and inform them if they are pregnant, may be pregnant or are breastfeeding. Therapeutic procedures can involve additional preparation and post-treatment instructions, including precautions around contact with other people. Patients should follow the specific instructions provided by their care team rather than assuming all nuclear medicine tests require the same preparation.

For most diagnostic nuclear medicine tests, the amount of radiation used is small and the benefits generally outweigh the potential risks when the test is medically appropriate. Minor effects such as discomfort at an injection site can occur, while allergic reactions are rare. Most diagnostic tracers leave the body naturally, often through urine, within a relatively short period. Therapeutic nuclear medicine uses higher doses and may require temporary precautions, such as limiting close contact with others or following specific hygiene instructions. Pregnancy and breastfeeding should always be discussed with the nuclear medicine team beforehand.